300 FORCING GARDEN. 



but their use has not hitherto become general. The ar- 

 rangement of the flues must depend upon the nature of the 

 house ; it may, however, be remarked generally, that, as 

 heated air has a tendency to ascend, they should be placed 

 as near as can conveniently be done to the front of the 

 house, where, of course, the sloping roof is lowest. It is 

 likewise important that the flue should be introduced, and 

 exert its greatest influence, at that point of the structure 

 which is most exposed to any refrigerating cause. 



The furnace is most properly situate behind the house, 

 and is generally covered by a shed. For the most part it 

 is constructed so that the upper part of its arch shall be on 

 a level with the top of the flue ; but where a considerable 

 heat is required, as in pine-apple stoves, it is found pre- 

 ferable to sink the furnace, in order to produce a neck or 

 rise of about a foot and a half in heigh th, which moderates 

 the intensity of the heat on its first entrance, and, by in- 

 creasing the draught, causes the fire to burn freely. The 

 size of the furnace must be regulated by the kind of fuel 

 employed. Where coke or charcoal is used, it may be 

 about eighteen inches square ; but where small coal, turf, 

 or peat is to be burned, it should be two feet, or even two 

 and a half square, by two feet in height. A large furnace 

 insures the long continuance of the fire, a fact which in 

 practice has received too little attention. To resist the 

 effects of heat, the interior should be lined with fire-brick. 

 The roof should be strongly arched. The door may be 

 about a foot square, and when it is double, as it ought al- 

 ways to be, the outer half should be a little larger than 

 the inner. The grate is of the same breadth as the door, 

 and may extend about two-thirds of the length of the fur- 

 nace. The ash-pit is equally wide, and from fifteen to 

 eighteen inches deep ; it is furnished with a ventilator in 



